For the last few years I, among others, have been looking at the news and wondering to what extent this, that or the other extreme weather event – the 2010 Russian heatwave, the Queensland floods, record flooding in Thailand, etc – was due to climate change. When I asked those who ought to know, the response was always, “There is probably some influence there but it is too hard to disentangle from natural variation, so you can’t just say that it was caused by global warming,” or words to that effect.
This week RealClimate reported on a scientific paper by Stefan Rahmstorf and Dim Coucou which puts statistically verifiable numbers on the feeling that, yes, global warming is making our weather more extreme. RealClimate’s report is a (relatively) non-technical introduction to the findings and it is linked to the paper itself if you want more.
My really short, really non-technical, summary is that the number of record-breaking events increases in proportion to the rate at which the normal (average) conditions are changing. That matches my gut feeling very well, which naturally pleases me. But it simultaneously alarms me because it means that record-breaking events are going to get more and more frequent unless we can quickly and radically reduce our CO2 emissions.
Back to the science: the authors applied their technique to the Russian heatwave and found, “an approximate 80% probability that the 2010 July heat record would not have occurred without climate warming.” That quote is from the abstract of the paper, meaning that it is in careful scientific language, i.e. there is an approximate 99.9% probability that they can back up every word of it.
The Comments on RealClimate posts are usually well worth reading. Two caught my eye this time:
(1) Comment 36: Ricky Rood looks at other ways in which the 2010 Russian heat wave was extreme:
The winter of 2010 and the spring of 2011 were characterized by very high food prices. An essay by Sarah Johnstone and Jeffrey Mazo entitled, Global Warming and Arab Spring, draws a convincing line that the pressure on food prices was a contributor to the start of the revolutions of the Arab Spring – the tumultuous uprising against many Arab governments. (also here) To diffuse the arguments that are sure to follow – this was a contributor, along with many other factors that came together to fuel a movement. This is the idea of climate extremes as a threat multiplier.
(2) Pete Dunkelberg says:
For a first approximation, an outlier [i.e. extreme event] in the direction of a trend tells you what’s coming. … Just from the shape of a bell curve (and this is far from original) one can see that you don’t have to move the mean very far in one direction for outliers on that side to become much more frequent. A one hundred year heat wave or flood readily becomes a ten or five year event. The new hundred year flood is going to drown people.
Now, how did that Chinese curse go? “May you live in interesting times” – was that it?